US 7521346 B2
A compound metal comprising HfSiN which is a n-type metal having a workfunction of about 4.0 to about 4.5, preferably about 4.3, eV which is thermally stable on a gate stack comprising a high k dielectric and an interfacial layer. Furthermore, after annealing the stack of HfSiN/high k dielectric/interfacial layer at a high temperature (on the order of about 1000° C.), there is a reduction of the interfacial layer, thus the gate stack produces a very small equivalent oxide thickness (12 Å classical), which cannot be achieved using TaSiN.
1. A method of forming a semiconductor structure comprising:
providing a stack comprising, from top to bottom, a Hf oxide high k dielectric and an interfacial layer on a surface of a substrate;
forming a HfSiN film on said stack, wherein said HfSiN film is formed by providing a Hf target and an atmosphere that comprises a mixture of Ar, N2, and a Si source diluted with from about 70 to 99% He and sputtering said HfSiN film from said Hf target in said atmosphere, wherein said Si source has the formula SiH4-nRn wherein n is 0, 1, 2, 3 or 4 and R is an aliphatic moiety containing from 1 to about 18 carbon atoms and the mixture of Ar, N2, and Si source has a flow rate from about 1-100/1-100/1-100 sccm, respectively;
forming a Si-containing conductive material atop said HfSiN film;
patterning said Si-containing conductive material, said HfSiN film and said stack into a patterned gate region; and
annealing said Si-containing conductive material, said HfSiN film and said stack utilizing a first anneal in nitrogen at 1000° C., followed by a second anneal in a forming gas ambient at 450° C. to provide a gate stack structure in which the thickness of the interfacial layer is reduced and said gate stack has an equivalent oxide thickness of about 12 angstroms.
This application is a divisional application of U.S. patent application Ser. No. 11/035,369, filed Jan. 13, 2005.
The present invention relates to a semiconductor device and a method of fabricating the same. More particularly, the present invention relates to a complementary metal oxide semiconductor (CMOS) device which includes a thermally stable n-type metal on a high dielectric constant, k/interfacial layer stack. The present invention also provides a process for forming the thermally stable n-type metal which can be integrated with a CMOS processing flow.
In standard CMOS devices, polysilicon is typically the standard gate material. The technology of fabricating CMOS devices using polysilicon gates has been in a constant state of development, and is now widely used in the semiconductor industry. One advantage of using polysilicon gates is that they can sustain high temperatures. However, there are also some problems associated with using a polysilicon gate. For example, due to the poly-depletion effect and relative high electrical sheet resistance (approximately 150 Ohms/Sq.), polySi gates commonly used in CMOS devices are becoming a gating factor in chip performance for channel lengths of 0.1 micron and below. Another problem with polySi gates is that the dopant in the polySi gate, such as boron, can easily diffuse through the thin gate dielectric causing further degradation of the device performance.
In order to avoid the problems with polySi gates, it has been suggested to replace the polySi gate with a single metal. Metals with different workfunctions, one for pFETs and one for nFETs are required for CMOS technologies using a high k dielectric. Metal/high k dielectric stacks also have to be subjected to a high temperature (on the order of about 1000° C.) anneals required for the source/drain self-aligned implant activation. Gate stack reactions occur during this high temperature anneal limiting the choice of materials. For example, in gate stacks including W and a high k dielectric, SiO2 regrowth occurs at the interface limiting inversion layer scalability. See, for example, A. Callegari, et al. IEDM 2004, p. 825, S. Francisco Calif., Dec. 13-15, 2004.
Metal compounds may be more stable, but still have problems with targeting the right workfunction. For example, TaSiN has been proposed as a nFET candidate, but still there are some questions about its workfunction and mobility reduction is observed in nFET devices. Furthermore, it appears that the inversion thickness scability is somewhat limited using TaSiN.
In view of the above, there is a need for providing a new compound metal which is thermally stable on a gate stack including a high k dielectric. In particular, there is a need for providing a new compound metal useful in nFET devices.
The present invention provides a new compound metal comprising HfSiN which is a n-type metal having a workfunction of about 3.7 to about 4.5 eV, preferably about 4.0, eV which is thermally stable on a gate stack comprising a high k dielectric and an interfacial layer. Furthermore, after annealing the stack of HfSiN/high k dielectric/interfacial layer at a high temperature (on the order of about 1000° C.), there is a reduction of the interfacial layer, thus the gate stack produces a very small equivalent oxide thickness (12 Å classical), which cannot be achieved using TaSiN.
In broad terms, the present invention provides a semiconductor structure, i.e., film stack, which comprises:
Additionally, the present invention provides a semiconductor structure that comprises:
In addition to the film stack and the semiconductor structure described above, the present invention also provides a method of fabricating a HfSiN metal compound that comprises:
In accordance with the present invention, the Si source diluted with He, which limits the Si source reactivity, improves the quality of the film. The resistivities of the HfSiN film can vary depending on the concentration of the process gases. Typically, the higher the nitrogen and/or Si concentrations, the higher the resistivity.
The present invention also provides a method of fabricating the semiconductor structure described above in which the inventive process for forming a HfSiN film is employed. In general terms, the semiconductor structure is formed by first providing a stack comprising a high k dielectric and an interfacial layer on a surface of a substrate; and thereafter forming a HfSiN film on said stack utilizing the processing steps mentioned above, i.e., by providing a Hf target and an atmosphere that comprises Ar/N2/a Si source that is diluted with He; and sputtering a HfSiN film from said Hf target in said atmosphere.
In some embodiments of the present invention, the HfSiN metal gate can be used alone as the gate electrode, or in conjunction with a Si-containing gate electrode that includes a silicide contact on an upper surface thereof. The later structure is referred to herein as a dual polySi/HfSiN-containing FET.
It is noted that the term high k dielectric is used throughout the present application to denote an insulator material whose dielectric constant k, is greater than SiO2, e.g., greater than 4.0. Preferably, the high k dielectric has a k that is about 7.0 or greater.
The term “interfacial layer” is used throughout the present application to denote an insulator material that comprises atoms of at least Si or O including, for example, SiO2, and SiON.
The present invention, which provides a HfSiN compound metal that can be used as a thermally stable n-metal gate on a stack comprising a high k dielectric and an interfacial layer as well as a method of fabricating the same, will now be described in greater detail by referring to the drawings that accompany the present application. It is noted that the drawings of the present invention are provided for illustrative purposes and thus they are not drawn to scale.
Reference is first made to
The semiconductor substrate 10 employed in the present invention comprises any semiconducting material including, but not limited to: Si, Ge, SiGe, SiC, SiGeC, Ga, GaAs, InAs, InP and all other IV/IV, III/V, or II/VI compound semiconductors. Semiconductor substrate 10 may also comprise an organic semiconductor or a layered semiconductor such as Si/SiGe, a silicon-on-insulator (SOI) or a SiGe-on-insulator (SGOI). In some embodiments of the present invention, it is preferred that the semiconductor substrate 10 be composed of a Si-containing semiconductor material, i.e., a semiconductor material that includes silicon. The semiconductor substrate 10 may be doped, undoped or contain doped and undoped regions therein.
The semiconductor substrate 10 may also include a first doped (n- or p-) region, and a second doped (n- or p-) region. For clarity, the doped regions are not specifically shown in the drawings of the present application. The first doped region and the second doped region may be the same, or they may have different conductivities and/or doping concentrations. These doped regions are known as “wells”. The semiconductor substrate 10 may be strained, unstrained or a combination thereof. Moreover, the semiconductor substrate 10 may have any crystallographic orientation including, for example, 100, 110, 111 or a combination thereof. Alternatively, the semiconductor substrate 10 may be a hybrid substrate that includes at least two planar surfaces of different crystallographic orientation.
At least one isolation region (not shown) is then typically formed into the semiconductor substrate 10. The isolation region may be a trench isolation region or a field oxide isolation region. The trench isolation region is formed utilizing a conventional trench isolation process well known to those skilled in the art. For example, lithography, etching and filling of the trench with a trench dielectric may be used in forming the trench isolation region. Optionally, a liner may be formed in the trench prior to trench fill, a densification step may be performed after the trench fill and a planarization process may follow the trench fill as well. The field oxide may be formed utilizing a so-called local oxidation of silicon process. Note that the at least one isolation region provides isolation between neighboring gate regions, typically required when the neighboring gates have opposite conductivities. The neighboring gate regions can have the same conductivity (i.e., both n- or p-type), or alternatively they can have different conductivities (i.e., one n-type and the other p-type).
Interfacial layer 12 is then formed atop the surface of the semiconductor substrate 10 utilizing a thermal process such as oxidation or oxynitridation, a deposition process such as chemical vapor deposition (CVD), plasma-assisted CVD, atomic layer deposition (ALD), evaporation, sputtering, and chemical solution deposition, or a combination thereof. Alternatively, a deposition process and nitridation can be used to form the interfacial layer 12. The interfacial layer 12 comprising atoms of at least Si and O, with N being optional. The interfacial layer 12 thus may comprise SiO2, SiON, silicates thereof, or multilayers thereof. In some embodiments, the interfacial layer 12 comprises SiO2, while in other embodiments the interfacial layer 12 comprises SiON. The interfacial layer 12 comprises from about 1 to about 80, typically from about 1 to about 30, atomic percent Si. The remaining is O and/or N. The Si can be continuously present throughout the interfacial layer 12 or it can be graded.
The interfacial layer 12 typically has a dielectric constant from about 4.0 to about 20, with a dielectric constant from about 4.5 to about 18 being even more typical. The interfacial layer 12 typically has a thickness from about 0.1 to about 5 nm, with a thickness from about 0.2 to about 2.5 nm being more typical.
Next, and as shown in
Illustratively, the high k dielectric 14 employed in the present invention includes, but is not limited to: an oxide, nitride, oxynitride, and/or silicate (including metal silicates and nitrided metal silicates). In one embodiment, it is preferred that the high k dielectric 14 is comprised of an oxide such as, for example, HfO2, ZrO2, Al2O3, TiO2, La2O3, SrTiO3, LaAlO3, Y2O3, Ga2O3, GdGaO and mixtures thereof. Highly preferred examples of the high k dielectric 14 include HfO2, hafnium silicate or hafnium silicon oxynitride.
The physical thickness of the high k dielectric 14 may vary, but typically, the high k dielectric 14 has a thickness from about 0.5 to about 10 nm, with a thickness from about 0.5 to about 3 nm being more typical.
After providing the stacked structure shown in
The Hf target used in the present invention includes any solid source of Hf. The silicon, Si source used in the atmosphere during the sputtering of the HfSiN film includes any organic containing Si compound including for example, SiH4-nRn wherein n is 0, 1, 2, 3, or 4, and R is an aliphatic moiety (i.e., alkane, alkene, alkyne or a combination thereof) containing from 1 to about 18, preferably from about 1 to about 8 carbon atoms. The aliphatic moiety can be straight chain or branched. Preferably, n is 0 and the Si source is SiH4. The source of Si can be a solid, liquid or gas, with gaseous Si sources being highly preferred.
The flow ratio of Ar/N2/Si source employed in the present invention is from about 1-100/1-100/1-100 sccm, respectively, with a flow ratio from about 10-20/5-15/10-30 sccm being even more typical. In some preferred embodiments, the flow ratio of Ar/N2/Si source from about 5/5/5 sccm to about 50/50/50 sccm, respectively can be employed.
The other sputtering conditions such as temperature, pressure and time are conventional and are well known to those skilled in the art.
As indicated above, the resistivity of the HfSiN film depends on the concentration of the process gases; the higher the nitrogen and/or Si concentration the higher the resistivity of the HfSiN film 16. Typically, the resistivity of the HfSiN film is about 105 micro-ohm/cm or less, with a resistivity from about 100 to about 130 micro-ohm/cm being even more typical.
The thickness of the HfSiN film 16 formed may vary depending on the sputtering conditions used and the type of device to be fabricated. Typically, the HfSiN film 16 has a thickness, after sputtering, from about 2 to about 200 nm, with a thickness from about 5 to about 40 nm being even more typical.
The structure shown in
In the embodiment illustrated in
The Si-containing material is typically doped utilizing an in-situ deposition process or by deposition, ion implantation and annealing. The dopant is a n-type dopant since HfSiN is a n-type metal. The thickness, i.e., height, of the Si-containing material 18 formed at this point of the present invention may vary depending on the process employed. Typically, the Si-containing material has a vertical thickness from about 20 to about 180 nm, with a thickness from about 40 to about 150 nm being more typical.
In the processing embodiment illustrated, the Si-containing material 18, the HfSiN layer 16, and optionally the high k dielectric 14 and the interfacial layer 12 are then patterned by lithography and etching so as to provide a patterned gate region or stack 20. Although a single patterned gate region (or stack) 20 is shown, the present invention contemplates forming a plurality of patterned gate regions (or stacks) 20. When a plurality of patterned gate regions (or stacks) are formed, the gate regions (or stacks) may have the same dimension, i.e., length, or they can have variable dimensions to improve device performance. Each patterned gate stack (or region) 20 at this point of the present invention includes at least a patterned HfSiN layer 16.
The lithographic step includes applying a photoresist to the upper surface of the blanket layered structure shown in either
Suitable dry etching processes that can be used in the present invention in forming the patterned gate region (or stack) 20 include, but are not limited to: reactive ion etching, ion beam etching, plasma etching or laser ablation. The dry etching process employed is typically, but not always, selective to the underlying high k dielectric 14 therefore this etching step does not typically remove the stack containing the high k dielectric 14 and the interfacial layer 12. In some embodiments and as shown in
Next, at least one spacer 22 is typically, but not always, formed on exposed sidewalls of each patterned gate region (or stack) 20, see, for example,
The width of the at least one spacer 22 must be sufficiently wide such that the source and drain silicide contacts (to be subsequently formed) do not encroach underneath the edges of the gate region (or stack) 20. Typically, the source/drain silicide does not encroach underneath the edges of the gate region (or stack) 20 when the at least one spacer 22 has a width, as measured at the bottom, from about 20 to about 80 nm.
The gate region (or stack) 20 can also be passivated prior to spacer formation by subjecting the same to a thermal oxidation, nitridation or oxynitridation process. The passivation step forms a thin layer of passivating material (not shown) about the gate region (or stack) 20. This step may be used instead or in conjunction with the previous step of spacer formation. When used with the spacer formation step, spacer formation occurs after the gate region (or stack) 20 passivation process.
Source/drain diffusion regions 24 (with or without the spacers present) are then formed into the substrate. The source/drain diffusion regions 24 are formed utilizing ion implantation and an annealing step. The annealing step serves to activate the dopants that were implanted by the previous implant step. The conditions for the ion implantation and annealing are well known to those skilled in the art. The structure formed after ion implantation and annealing is shown in
The source/drain diffusion regions 24 may also include extension implant regions (not separately labeled) which are formed prior to source/drain implantation using a conventional extension implant. The extension implant may be followed by an activation anneal, or alternatively the dopants implanted during the extension implant and the source/drain implant can be activated using the same activation anneal cycle. Halo implants (not shown) are also contemplated herein. The source/drain extensions are typically shallower than the deep source/drain regions and they include an edge that is aligned with an edge of the patterned gate region (or stack) 20.
Next, and if not previously removed, the exposed portion of the high k dielectric 14 and the underlying interfacial layer 12 are removed utilizing a chemical etching process that selectively removes these insulating materials. This etching step stops on an upper surface of the semiconductor substrate 10. Although any chemical etchant may be used in removing the exposed portions of the high k dielectric 14 and the underlying interfacial layer 12, in one embodiment dilute hydrofluoric acid (DHF) is used.
The silicidation process comprises forming a conductive and refractory metal such as Co, Ti, W, Ni, Pt or alloys thereof with other alloying additives, such as C, Ge, Si, and etc., on top of the area to be silicided. A conventional deposition process, such as CVD, PECVD, sputtering, evaporation or plating, can be used. Optionally, a barrier layer may be formed over the metal layer that protects the metal from oxidation. Examples of optional barrier layers include, for example, SiN, TiN, TaN, TiON and combinations thereof. Following metal deposition the structure is subjected to at least a first anneal that causes reaction between the deposited metal and Si and subsequent formation of a metal silicide. The annealing is typically performed at a temperature from about 250° to about 800° C., with a first annealing temperature from about 400° to about 550° C. being more typical.
In some embodiments, the first anneal forms a metal rich silicide phase, which is highly resistant to a selective etch process. When a metal rich phase is produced, a second higher temperature anneal is required to form a low resistivity silicide. In other embodiments, the first anneal is sufficient in forming the low resistivity silicide.
Following the first anneal, the unreacted and remaining portions of the deposited metal are removed using a conventional etch process, such as wet etching, reactive-ion etching (RIE), ion beam etching, or plasma etching.
If needed, a second anneal is performed after the etching process. The second annealing is typically performed at higher temperatures than the first annealing. A typical temperature range for the second, optional, anneal is from about 550° to about 900° C.
Further CMOS processing such as the formation of BEOL (back-end-of-the-line) interconnect levels with metal interconnects can be formed utilizing processing steps that are well known to those skilled in the art.
The following example provides an illustration of the inventive process as well as some advantages that can be obtained from using the same in forming a HfSiN-containing gate stack.
In this example, a HfSiN/HfO2/SiO2 stack was formed on a surface of a Si wafer. The SiO2 interfacial layer was formed by oxidation of the Si wafer. The thickness of the SiO2 interfacial layer was about 1 nm. A HfO2 dielectric having a thickness of about 3 nm was then formed on the SiO2 interfacial layer by ALD. The HfSiN layer was then formed by providing a Hf target and an atmosphere comprising Ar/N2/SiH4(2% in He) in which flow ratio of Ar:N2:SiH4 (2% in He) was 20:10:20 sccm, respectively. The HfSiN layer had a thickness of about 40 nm. After providing the stack, the stack was subjected to a 1000° C. anneal, followed by a forming gas anneal that was performed at 450° C. For comparison, a TaSiN compound metal was formed about a similar HfO2/SiO2 stack.
While the present invention has been particularly shown and described with respect to preferred embodiments thereof it will be understood by those skilled in the art that the foregoing and other changes in forms and details may be made without departing from the spirit and scope of the present invention. It is therefore intended that the present invention not be limited to the exact forms and details described and illustrated, but fall within the scope of the appended claims.